WO2020219022A1

WO2020219022A1 - Heat pipes for electronic devices

Info

Publication number: WO2020219022A1
Application number: PCT/US2019/028643
Authority: WO
Inventors: Kuan-Ting Wu; Chi Hao Chang; Chih-Wei Huang
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2019-04-23
Filing date: 2019-04-23
Publication date: 2020-10-29
Also published as: TW202040080A

Abstract

A heat pipe can include a mechanical support structure having a channel extending from an exterior surface to an interior surface opposite the exterior surface. The interior surface can define an interior cavity and the mechanical support structure can include an amorphous metal. A thermally conductive material can extend through the mechanical support structure from the exterior surface to the interior surface via the channel. The thermally conductive material can also line the interior cavity and form a vapor chamber. A working fluid can be sealed within the vapor chamber.

Description

HEAT PIPES FOR ELECTRONIC DEVICES

BACKGROUND

[0001 ] Electronic devices and circuitry can generate excess heat. Appropriate heat management can improve reliability of electronic devices and can prevent premature failure. Accordingly, a variety of heat transfer methodologies have been developed to manage the excess heat generated by these electronic devices and circuitry. Non-limiting examples can include heat sinks, cold plates, convective air cooling, forced air cooling, heat pipes, Peltier cooling plates, etc.

[0002] As one specific example, a heat pipe generally operates on the principle of repeated or continuous evaporation and condensation of a working fluid. More specifically, heat input vaporizes a liquid component of the working fluid inside an evaporator section of the heat pipe. The vapor flows towards the colder condenser section of the heat pipe, where the vapor condenses and gives up its latent heat. The condensed liquid returns to the evaporator and the two-phase flow circulation continues while a temperature gradient is maintained between the evaporator and the condenser.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] FIG. 1 A is a cross-sectional view of a mechanical support structure in accordance with the present disclosure;

[0004] FIG. 1 B is a cross-sectional view of a heat pipe in accordance with the present disclosure;

[0005] FIG. 2 is a flow diagram of a method of manufacturing a heat pipe in accordance with the present disclosure; and [0006] FIG. 3 is a schematic representation of an electronic device in accordance with the present disclosure.

DETAILED DESCRIPTION

[0007] As electronic devices become smaller and thinner, there is an increasing demand for smaller and thinner heat management components. In some cases, heat management components can become mechanically weak and can become more easily damageable and prone to breakage as they become thin. This can compromise the lifetime and effectiveness of these components. The present disclosure is directed to heat pipes that can be thin, while maintaining good mechanical integrity.

[0008] In one example, a heat pipe can include a mechanical support structure having a channel extending from an exterior surface to an interior surface opposite the exterior surface, the interior surface defining an interior cavity, and the mechanical support structure including an amorphous metal; a thermally conductive material extending through the mechanical support structure from the exterior surface to the interior surface via the channel, the thermally conductive material also lining the interior cavity and forming a vapor chamber; and a working fluid sealed within the vapor chamber. In some examples, the amorphous metal can have a flexural strength of from about 500 megapascals (MPa) to about 1700 MPa. In some additional examples, the amorphous metal can include aluminum, titanium, vanadium, manganese, chromium, zirconium, tin, or an alloy thereof. In some examples, the thermally conductive material can include a material having a thermal conductivity of from about 180 watts per meter- kelvin (W/mK) to about 500 W/mK. In some further examples, the thermally conductive material can include copper, silver, gold, aluminum, or an alloy thereof. In some examples, the working fluid can have a latent heat of evaporation of from about 800 kilojoules per kilogram (kJ/kg) to about 2500 kJ/kg. In some additional examples, the working fluid can include water, ammonia, methanol, ethanol, glycerol, or a combination thereof.

[0009] In another example, a method of manufacturing a heat pipe can include shaping an amorphous metal to form a mechanical support structure having a channel extending from an exterior surface to an interior surface opposite the exterior surface, the interior surface defining an interior cavity; introducing a thermally conductive material to the interior cavity via the channel, the thermally conductive material lining the interior cavity to form a vapor cavity; introducing a working fluid to the vapor cavity; and sealing the vapor cavity to form a vapor chamber. In some examples, the mechanical support structure can have an outer diameter of from about 2 millimeters (mm) to about 10 mm. In some additional examples, wherein the mechanical support structure can have an inner diameter of from about 1.5 mm to about 8 mm. In still additional examples, the thermally conductive material lining the interior cavity can have a thickness of from about 0.2 mm to about 0.8 mm. In some further examples, introducing the thermally conductive material can be performed by die casting or injection molding.

In still further examples, the vapor chamber can have a length of from about 50 mm to about 500 mm.

[0010] In yet another example, an electronic device can include a heat

generating component and a heat pipe positioned to transfer heat away from the heat generating component. The heat pipe can include a mechanical support structure having a channel extending from an exterior surface to an interior surface opposite the exterior surface, the interior surface defining an interior cavity, and the mechanical support structure including an amorphous metal, a thermally conductive material extending through the mechanical support structure from the exterior surface to the interior surface via the channel, the thermally conductive material lining the interior cavity and forming a vapor chamber, and a working fluid sealed within the vapor chamber. In some examples, the electronic device can include a display, an amplifier, a memory device, a server, a modem, a router, a personal computer, a laptop computer, a tablet, a phone, a speaker, a television, a media player, a projector, a smart device, or a combination thereof.

[0011 ] In addition to the examples described above, the heat pipes, methods of manufacturing heat pipes, and electronic devices will be described in greater detail below. It is also noted that when discussing the heat pipes, methods of manufacturing heat pipes, and electronic devices described herein, these relative discussions can be considered applicable to the other examples, whether or not they are explicitly discussed in the context of that example. Thus, for example, in discussing a mechanical support structure related to a heat pipe, such disclosure is also relevant to and directly supported in the context of the methods of manufacturing heat pipes and electronic devices described herein, and vice versa.

Mechanical Support Structures

[0012] In further detail, the heat pipes disclosed herein can include a mechanical support structure. As described previously, as the heat pipe becomes thinner, the mechanical integrity of the heat pipe can be compromised. Thus, the mechanical support structure can allow the heat pipe to be thin while maintaining good mechanical integrity.

[0013] The mechanical support structure can generally be made of or include an amorphous metal. Amorphous metals have a variety of properties that can make them suitable for use in a mechanical support structure. For example, amorphous metals can have good mechanical strength while maintaining good elasticity. Further, amorphous metals can be formed into a variety of shapes, including complex shapes. As such, amorphous metals can be formed into a suitable backbone structure for a thin thermally conductive film or material.

[0014] With this in mind, amorphous metals that are suitable for use as the mechanical support structure can typically have a flexural strength of from about 500 megapascals (MPa) to about 1700 MPa. In other examples, the amorphous metal can have a flexural strength of from about 500 MPa to about 1000 MPa, from about 800 MPa to about 1300 MPa, or from about 1200 MPa to about 1700 MPa. Flexural strength can be measured by a variety of test methods, such as ASTM D790. Per ASTM D790, a bar of rectangular cross section is positioned to be suspended across two supports at a span-to-depth ratio of about 16:1. A load is applied midway between the supports at a strain rate of about 0.01 mm/mm/min until rupture occurs or until a strain of about 5.0% is reached, whichever occurs first.

[0015] In some specific examples, the amorphous metal can be or include aluminum, titanium, vanadium, manganese, chromium, zirconium, tin, the like, or a combination thereof. In some examples, the amorphous metal can be or include aluminum or an alloy thereof. In some additional examples, the amorphous metal can be or include titanium or an alloy thereof. In still additional examples, the amorphous metal can be or include vanadium or an alloy thereof. In some further examples, the amorphous metal can be or include manganese or an alloy thereof. In yet further examples, the amorphous metal can be or include chromium or an alloy thereof. In still further examples, the amorphous metal can be or include zirconium or an alloy thereof. In yet additional examples, the amorphous metal can be or include tin or an alloy thereof.

Thermally Conductive Materials

[0016] A variety of thermally conductive materials can be employed in the disclosed heat pipes. Generally, the thermally conductive materials can have a high thermal conductivity and can be suitable for die casting or injection molding into the mechanical support structure without adversely affecting the integrity of the mechanical support structure. In some examples, the thermally conductive material can be or include a material having a thermal conductivity of from about 180 watts per meter- kelvin (W/mK) to about 500 W/mK. In some additional examples, the thermally conductive material can be or include a material having a thermal conductivity of from about 180 W/mK to about 300 W/mK, from about 250 W/mK to about 350 W/mK, from about 300 W/mK to about 400 W/mK, from about 350 W/mK to about 450 W/mK, or from about 400 W/mK to about 500 W/mK. It is emphasized that these thermal conductivity values refer to the thermal conductivity rating for the material itself, not the heat pipe. For example, pure copper has a thermal conductivity of about 401 W/mK. In contrast, the thermal conductivity of a copper heat pipe can vary depending on the length thereof, which will be discussed in greater detail below.

[0017] In some specific examples, the thermally conductive material can be or include copper, silver, gold, aluminum, the like, or an alloy thereof. In some examples, the thermally conductive material can be or include copper or an alloy thereof. In some additional examples, the thermally conductive material can be or include silver or an alloy thereof. In yet additional examples, the thermally conductive material can be or include gold or an alloy thereof. In still additional examples, the thermally conductive material can be or include aluminum or an alloy thereof. It is noted that the mechanical support structure and the thermally conductive material are generally different materials.

Working Fluids

[0018] A variety of working fluids can be employed in the heat pipe. Working fluids can be chosen based on the temperature at which the heat pipe is intended to operate. For example, the working fluid can be selected from fluids that are compatible with the thermally conductive material of the heat pipe and that will provide both a vapor phase and a liquid phase over the intended operating temperature range. Additionally, the working fluid can typically have a high latent heat of evaporation. In some examples, the working fluid can have a latent heat of evaporation of from about 800 kilojoules per kilogram (kJ/kg) to about 2500 kJ/kg. In some further examples, the working fluid can have a latent heat of evaporation of from about 800 kJ/kg to about 1500 kJ/kg, from about 1200 kJ/kg to about 1800 kJ/kg, from about 1500 kJ/kg to about 2000 kJ/kg, from about 1800 kJ/kg to about 2200 kJ/kg, or from about 2000 kJ/kg to about 2500 kJ/kg.

[0019] In some specific examples, the working fluid can be or include water, ammonia, methanol, ethanol, glycerol, the like, or a combination thereof. In some examples, the working fluid can be or include water. In some additional examples, the working fluid can be or include ammonia. In yet additional examples, the working fluid can be or include methanol. In still additional examples, the working fluid can be or include ethanol. In some further examples, the working fluid can be or include glycerol.

It is noted that not all working fluids are compatible with all thermally conductive materials. For example, a water working fluid may not be compatible with a vapor chamber formed of aluminum. Flowever, a water working fluid is generally compatible with a vapor chamber formed of copper and an ammonia working fluid is generally compatible with a vapor chamber formed of aluminum, for example.

Methods of Manufacturing

[0020] The methods of manufacturing heat pipes generally include shaping an amorphous metal to form a mechanical support structure having a channel extending from an exterior surface to an interior surface opposite the exterior surface. The interior surface can define an interior cavity. The mechanical support structure can be shaped by molding or other suitable process. For example, an amorphous metal ingot can be melted and loaded into a mold, such as by injection molding or other suitable molding process, to form an amorphous metal mechanical support structure.

[0021 ] One example of a mechanical support structure is illustrated in FIG. 1A. More specifically, FIG. 1A illustrates heat pipe 100 after shaping an amorphous metal to form a mechanical support structure 110, but prior to introducing the thermally

conductive material. The mechanical support structure can be considered a backbone structure for the heat pipe. A channel 112 can extend from an exterior surface 114 to an interior surface 116 of the mechanical support structure. The interior surface can define an interior cavity 118. In some examples, a core or central component 111 can be included within the interior cavity. The core or central component can help shape the thermally conductive material when it is introduced to the mechanical support structure. In other examples, the interior cavity can be devoid of a core or central component. Where this is the case, the thermally conductive material can fill the entire interior cavity. The channel can facilitate introduction of the thermally conductive material into the interior cavity. Further, thermally conductive material extending from the inner cavity to the exterior surface can provide additional mechanical interaction with the mechanical support structure and can serve as a thermal conduit for heat transfer.

[0022] Turning to FIG. 1 B, after the mechanical support structure 110 is formed, a thermally conductive material 120 can be introduced to the interior cavity 118 via channel 1 12. Generally, the thermally conductive material can be introduced to the mechanical support structure using die casting, injection molding, or other suitable process. In some further examples, the thermally conductive material can be degated after introducing into the mechanical support substrate to remove excess or waste portions of the thermally conductive material. Any suitable degating process can be employed. The thermally conductive material can line the interior cavity to form a vapor cavity (i.e. , vapor chamber 130 prior to sealing). In some examples, the core or central component 111 (See FIG. 1A) can facilitate shaping of the thermally conductive material for form a liner about the interior surface of the mechanical support structure to form the vapor cavity. The core or central component can then be removed by a suitable process(es), such as melting, laser etching, the like, or a combination thereof. In other examples, the interior cavity does not include a core or central component and can be filled entirely with thermally conductive material. A portion of the thermally conductive material can be removed to shape the thermally conductive material to form a liner about the interior surface of the mechanical support structure to form the vapor cavity.

[0023] A working fluid 140 can be introduced into the vapor cavity and the vapor cavity can be sealed to form a vapor chamber 130. It is noted that introducing the working fluid into the vapor cavity can include additional steps such as evacuating or driving other fluids out of the vapor chamber. In some specific examples, this can be performed by employing a vacuum pump or introducing working fluid into the vapor chamber and boiling the working fluid to drive other fluids out of the vapor chamber immediately prior to sealing the vapor chamber. Such processes can help facilitate proper heat management via the heat pipe, as contaminating fluids can interfere with proper functioning of the two-phase evaporation-condensation cycle within the vapor chamber. Any suitable sealing process can be employed. The sealing process can be in the form of hermetically sealing the vapor cavity to form a vapor chamber that is air tight, e.g., forming a hermetic seal.

[0024] As illustrated in FIG. 1 B, a hot surface of the heat pipe 100 (e.g., at the left-hand side of FIG. 1 B) can turn liquid working fluid 140 into a vapor by absorbing heat from the hot surface. The vapor can then travel along the heat pipe to a cooler interface (e.g., at the right-hand side of FIG. 1 B) where it can condense back into a liquid and release latent heat. The liquid working fluid can then return to the hot surface and the cycle can continue while a thermal gradient is maintained between the hot region (evaporator region) and cooler region (condenser region) of the heat pipe. In some examples, the liquid can travel from the condenser region via capillary action (e.g., via grooves formed in the interior surface of the vapor chamber 130, or the like), gravity, the like, or a combination thereof.

[0025] With reference to FIGs. 1A and 1 B, the heat pipe 100 can be

manufactured to have a variety of dimensions. The outer diameter OD or overall thickness of the heat pipe or mechanical support structure 110 can generally be from about 2 mm to about 10 mm. In some specific examples, the outer diameter of the heat pipe or mechanical support structure can be from about 2 mm to about 6 mm, from about 4 mm to about 8 mm, or from about 6 mm to about 10 mm.

[0026] The inner diameter ID of the mechanical support structure 110 can also have a variety of dimensions. The inner diameter generally refers to the shortest distance between oppositely positioned interior surfaces 116 of the mechanical support structure. Depending on the shape and design of the vapor cavity 130, the inner diameter may be uniform throughout the vapor cavity or it may vary depending on the location within the vapor cavity. The inner diameter can typically be from about 1.5 mm to about 8 mm. In other examples, the inner diameter can be from about 1.5 mm to about 5 mm, from about 3 mm to about 6 mm, from about 4 mm to about 7 mm, or from about 5 mm to about 8 mm.

[0027] The length L of the heat pipe 100 can determine the overall thermal conductivity of the heat pipe. Thus, the length of the heat pipe can vary depending on the particular application of the heat pipe and the associated thermal management requirements for the application. Typically, the heat pipe can have a length of from about 50 mm to about 500 mm. In some examples, the heat pipe can have a length of from about 50 mm to about 150 mm, from about 100 mm to about 200 mm, from about 150 mm to about 250 mm, from about 200 mm to about 300 mm, from about 250 mm to about 350 mm, from about 300 mm to about 400 mm, from about 350 mm to about 450 mm, or from about 400 mm to about 500 mm. In some examples, depending on the length of the heat pipe and the thermally conductive material employed, the heat pipe can have a thermal conductivity of from about 10,000 W/mK to about 100,000 W/mK, for example.

[0028] The thickness T of the thermally conductive material 120 lining the interior cavity 118 can generally be from about 0.2 mm to about 0.8 mm. In some examples, the thickness of the thermally conductive material lining the interior cavity can be from about 0.2 mm to about 0.4 mm, from about 0.3 mm to about 0.5 mm, from about 0.4 mm to about 0.6 mm, from about 0.5 mm to about 0.7 mm, or from about 0.6 mm to about 0.8 mm. The thickness of the liner refers to the thickness of the thermally conductive material between the interior surface 116 of the mechanical support structure 110 and the interior surface of the vapor chamber 130.

[0029] FIG. 2 presents a flow diagram of an example method 200 of

manufacturing a heat pipe. The method can include shaping 210 an amorphous metal to form a mechanical support structure having a channel extending from an exterior surface to an interior surface opposite the exterior surface, the interior surface defining an interior cavity. The method can also include introducing 220 a thermally conductive material to the interior cavity via the channel, the thermally conductive material lining the interior cavity to form a vapor cavity. Additionally, the method can include introducing 230 a working fluid to the vapor cavity and sealing 240 the vapor cavity to form a vapor chamber.

Electronic Devices

[0030] The heat pipes disclosed herein can be used in a variety of electronic devices. Non-limiting examples can include a display, an amplifier, a memory device, a server, a modem, a router, a personal computer, a laptop computer, a tablet, a phone, a speaker, a television, a media player, a projector, a smart device, the like, or a combination thereof.

[0031 ] In further detail, the electronic device can include a heat-generating component. For example, with demands for improved speeds and smaller sizes of electronic devices, microprocessors are becoming smaller with more compressed cores. This can cause higher rates of heat generation per unit area of the

microprocessor. As another example, temperatures can increase with smaller transistor designs because smaller channel dimensions can increase the power density and electron-phonon nonequilibrium within devices, for example. Further still, increasing temperatures can result from increasing numbers of metal layers in interconnects between transistors, resulting in increased current densities and aspect ratios. Thus, a variety of components, including increasingly smaller components, in electronic devices can generate high amounts of heat that can benefit from thermal management via a heat pipe. Accordingly, a heat pipe as described herein can be positioned to transfer heat away from a heat-generating component of the electronic device.

[0032] One schematic representation of an electronic device 390 is illustrated in FIG. 3. The electronic device can include a heat-generating component 380 and a heat pipe 300, as described herein, to transfer heat away from the heat-generating device. Thus, a working fluid within the heat pipe can be heated to evaporate a portion of the working fluid in an evaporator region proximate the heat-generating device (e.g., on the left-hand side of FIG. 3). The vapor can then travel to a cooler region (condenser region) of the heat pipe where it can condense back into a liquid (e.g., on the right-hand side of FIG. 3). In some examples, the condenser region can be cooled by a cooling component, such as a fan, a Peltier heat pump, the like, or a combination thereof to facilitate condensation of the liquid in the condenser region, although this is not required. A fan 370 is depicted in FIG. 3, but other cooling components can also be used, as desired.

Definitions

[0033] It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise.

[0034] As used herein, the term“about” is used to provide flexibility to a numerical range endpoint by providing that a given value may be“a little above” or“a little below” the endpoint. The degree of flexibility of this term can be dictated by the particular variable and would be within the knowledge of those in the field technology determine based on experience and the associated description herein.

[0035] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience.

Flowever, these lists should be construed as though individual members of the list are individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. [0036] Concentrations, dimensions, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also all the individual numerical values or sub-ranges encompassed within that range as if individual numerical values and sub-ranges are explicitly recited. For example, an atomic ratio range of about 1 at% to about 20 at% should be interpreted to include not only the explicitly recited limits of about 1 at% and about 20 at%, but also to include individual atomic percentages such as 2 at%, 11 at%, 14 at%, and sub-ranges such as 10 at% to 20 at%, 5 at% to 15 at%, etc.

[0037] The terms, descriptions, and figures used herein are set forth by way of illustration and are not meant as limitations. Many variations are possible within the disclosure, which is intended to be defined by the following claims -- and equivalents -- in which all terms are meant in the broadest reasonable sense unless otherwise indicated.

Claims

CLAIMS What is Claimed Is:

1. A heat pipe, comprising:

a mechanical support structure having a channel extending from an exterior surface to an interior surface opposite the exterior surface, said interior surface defining an interior cavity, and said mechanical support structure comprising an amorphous metal;

a thermally conductive material extending through the mechanical support structure from the exterior surface to the interior surface via the channel, said thermally conductive material also lining the interior cavity and forming a vapor chamber; and a working fluid sealed within the vapor chamber.

2. The heat pipe of claim 1 , wherein the amorphous metal has a flexural strength of from about 500 megapascals (MPa) to about 1700 MPa.

3. The heat pipe of claim 1 , wherein the amorphous metal comprises aluminum, titanium, vanadium, manganese, chromium, zirconium, tin, or an alloy thereof.

4. The heat pipe of claim 1 , wherein the thermally conductive material comprises a material having a thermal conductivity of from about 180 watts per meter-kelvin (W/mK) to about 500 W/mK.

5. The heat pipe of claim 1 , wherein the thermally conductive material comprises copper, silver, gold, aluminum, or an alloy thereof.

6. The heat pipe of claim 1 , wherein the working fluid has a latent heat of evaporation of from about 800 kilojoules per kilogram (kJ/kg) to about 2500 kJ/kg.

7. The heat pipe of claim 1 , wherein the working fluid comprises water, ammonia, methanol, ethanol, glycerol, or a combination thereof.

8. A method of manufacturing a heat pipe, comprising:

shaping an amorphous metal to form a mechanical support structure having a channel extending from an exterior surface to an interior surface opposite the exterior surface, said interior surface defining an interior cavity;

introducing a thermally conductive material to the interior cavity via the channel, said thermally conductive material lining the interior cavity to form a vapor cavity;

introducing a working fluid to the vapor cavity; and

sealing the vapor cavity to form a vapor chamber.

9. The method of claim 8, wherein the mechanical support structure has an outer diameter of from about 2 millimeters (mm) to about 10 mm.

10. The method of claim 8, wherein the mechanical support structure has an inner diameter of from about 1.5 mm to about 8 mm.

11. The method of claim 8, wherein the thermally conductive material lining the interior cavity has a thickness of from about 0.2 mm to about 0.8 mm.

12. The method of claim 8, wherein introducing the thermally conductive material is performed by die casting or injection molding.

13. The method of claim 8, wherein the vapor chamber has a length of from about 50 mm to about 500 mm.

14. An electronic device, comprising:

a heat-generating component; and

a heat pipe positioned to transfer heat away from the heat-generating

component, said heat pipe comprising: a mechanical support structure having a channel extending from an exterior surface to an interior surface opposite the exterior surface, said interior surface defining an interior cavity, and said mechanical support structure comprising an amorphous metal,

a thermally conductive material extending through the mechanical support structure from the exterior surface to the interior surface via the channel, said thermally conductive material lining the interior cavity and forming a vapor chamber, and

a working fluid sealed within the vapor chamber.

15. The electronic device of claim 14, wherein the electronic device comprises a display, an amplifier, a memory device, a server, a modem, a router, a personal computer, a laptop computer, a tablet, a phone, a speaker, a television, a media player, a projector, a smart device, or a combination thereof.